Biol172_Chapter50_handout

Biol172_Chapter50_handout - Chapter 49 Sensory Sensory...

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1 Chapter 49 Sensory Systems Sensory organs mediate the responses of animals to changes in the environment Avoidance of unfavorable conditions, enemies Attraction to food sources, mates Sensory Systems Most stimuli represent forms of energy the biological process of sensation involves converting this energy into a involves converting this energy into a change in the membrane potential of sensory receptors Sensory Transduction Sensory receptors receive stimuli in the form of energy Energy has a particular physical quality Signal has to be transduced into a signal that can be transmitted and integrated in the nervous system Stimuli are Energy Light Heat Sound Touch Gravity Pressure Magnetism Electric fields Chemical qualities = smell, taste, oxygen Stimuli are Energy Light photoreceptors Heat thermoreceptors Sound auditory receptors Touch proprioreceptors Gravity Pressure baroreceptors Magnetism Electric fields electroreceptors Chemical qualities olfactory receptors
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2 Only a small part of the energy spectrum can be perceived Sensory receptors transduce stimulus energy and transmit signals to the central nervous system Sensations are action potentials That reach the brain via sensory neurons Once the brain is aware of sensations It interprets them, giving the perception of stimuli Sensory Receptor Types Sensations and perceptions Begin with sensory reception, the detection of stimuli by sensory receptors Exteroreceptors Detect stimuli coming from the outside of the body Interoreceptors Detect internal stimuli Functions Performed by Sensory Receptors All stimuli represent forms of energy Sensation involves converting this energy Into a change in the membrane potential of sensory receptors This change in the membrane potential is known as a receptor potential Functions Performed by Sensory Receptors Sensory receptors perform four functions in this process: 1 Sensory transduction 1. 2. Amplification 3. Transmission 4. Integration Stimulus (energy) Receptor potential Transduction Action potential Transmission Integration Central nervous system Amplification
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3 Two types of sensory receptors exemplify these functions Stretch receptor in a crayfish muscle Muscle Weak muscle stretch Strong muscle stretch Dendrites Stretch receptor Axon Membrane potential (mV) –50 –70 0 –70 012 34567 Time (sec) Action potentials Receptor potential –50 –70 0 –70 01234567 Time (sec) Vertebrate Hair Cells –50 –70 Action potentials No fluid movement –50 –70 Receptor potential Fluid moving in one direction –50 –70 Fluid moving in other direction mbrane ntial (mV) “Hairs” of hair cel Neuro- trans- mit er at synapse Axon Less neuro- trans- mit er More neuro- trans- mit er 0 –70 Time (sec) 0 –70 Time (sec) 0 –70 Time (sec) Mem poten Me pote M e Sensory receptors can be extremely sensitive Ability to detect the smallest physical unit of stimulus possible
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Biol172_Chapter50_handout - Chapter 49 Sensory Sensory...

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